In the assembly of machines having a rotor rotatable relative to a stator, it is necessary to axially locate the rotor relative to the stator. In large dynamoelectric machines such as generators and motors, many parts must be assembled and the cumulative tolerance of errors makes the assembly difficult so as to have the rotor in proper position relative to the stator. These cumulative tolerances may include as many as fifteen or more tolerances which easily can be cumulative to the point that the rotor is out of proper position upon assembly. Additionally, in dynamoelectric machines there is a solenoid effect wherein even if the rotor were mechanically centered within the stator, there could still be a difference between the mechanical center position of the rotor and the magnetic center. This can be due to differences in air gap along the length of the rotor and can be due to manufacturing tolerances in the magnetic assembly of the rotor and stator. Accordingly, the machine must be electromagnetically operated in order to determine if the magnetic center is axially displaced from the mechanical center. These two main problems mean that in many cases a dynamoelectric machine, once having been assembled, is found to have an improper end play, that is, an improper clearance between the bearing and the rotor. Generally the machine is one having two bearings, one at each end. In a machine not designed for resisting an axial thrust and thus having only radial bearings, there is usually a small amount of clearance between a shaft shoulder and a bearing shoulder at each of the two bearings. Now if, due to cumulative tolerances or due to the magnetic center not coinciding with the mechanical center, the rotor and shaft assembly is displaced axially, then there is an improperly small clearance between the bearing and shaft shoulders at one end and an improperly large clearance at the other end of the machine.
Many dynamoelectric machines comprise a stack of rotor laminations on a shaft and comprise a stack of stator laminations in the frame. To attempt to achieve proper centering of the rotor shaft assembly in the bearings, the prior art often tried to move the stator within the frame but this was difficult in view of the usual press fit. Other prior attempts included trying to move the rotor laminations on the shaft but this was also difficult because of either a press fit or a shrink fit. Also either of these two methods of relocating meant that the entire dynamoelectric machine had to be disassembled in order to use a press on the stator or the rotor laminations.
Still other prior art attempts at locating the rotor and shaft assembly provided washer like shims on the shaft between the rotor or shaft shoulder and the inner end of the bearing in the frame. However, use of such washer like shims also meant that the dynamoelectric machine had to be disassembled in order to apply shims at one end and remove them from the other end. Another prior art attempt at axial end play adjustment was to force a thrust bearing unit into a cup shaped spacer with both being on the shaft between the rotor and the inner end of the bearing. However in this method there was no way nor any attempt to change the axial spacing once these two parts had initially been assembled.
Accordingly an object of the invention is to provide an axial adjustment to the rotor of a machine which obviates the above-mentioned disadvantages.
Another object of the invention is to provide axial adjustment to the rotor of a machine wherein there is relative axial positioning between a bearing and one of the rotor and stator.
Another object of the invention is to provide a method of adjusting the axial end play of a dynamoelectric machine without disassembly of the rotor from the stator.
Another object of the invention is to provide a means to locate a bearing relative to the frame of a rotating machine and then a means to secure the bearing and locator means in place.
The invention may be incorporated in the method of adjusting the axial end-play of a shaft-mounted rotor and a stator in a dynamoelectric machine having the stator in a frame receiving a bearing, said method comprising the steps of, providing in the frame bearing receiving means of an axial length to receive the bearing, assembling the machine and running the machine to cause the rotor and shaft assembly to have any axial shift due to magnetic action with the stator, stopping the machine, and relatively axially locating the bearing and one of the rotor and stator.
Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing.